Extracorporeal Lung Support in Trauma Patients

The rationale, indications and challenges of extracorporeal lung assist in trauma patients with severe acute respiratory distress syndrome is given on the basis of clinical and scientific experience.

Traumatic lung injury is often present in multiple trauma
with a wide spectrum of severity. In a large cohort study, patients with
multiple trauma were reported to suffer from acute hypoxaemia in 64% of cases
(Howard et al. 2015), 46% of whom developed the acute respiratory distress syndrome
(ARDS) (Ferguson et al. 2012). ARDS is characterised by a life-threatening
impairment of the pulmonary gas exchange, resulting in hypoxaemia, hypercapnia
and respiratory acidosis and requiring acute rescue measures (intubation and
lung protective mechanical ventilation, adequate positive end-expiratory pressure
(PEEP), positioning manoeuvres). Therapeutic advantages in the critical
management of severe trauma or thoracic injuries have been made, but these
diagnoses present a challenge and are still associated with increased mortality
and morbidity (Shah et al. 2008). Mechanical ventilation can damage the lungs and
initiate an inflammatory response contributing to extrapulmonary organ
dysfunction or triggering multiple organ failure. In trauma patients with
critical respiratory insufficiency a benefit from rescue extracorporeal lung support
(ELS) is discussed.

Technique and
Rationale for Extracorporeal Lung Support

Venovenous extracorporeal membrane oxygenation (vvECMO) is
used with an increasing tendency to avoid critical oxygenation impairment, and
to reduce harm from ventilation in patients with severe ARDS (Del Sorbo et al. 2014).
In principle, during ECMO a pump is integrated in an extracorporeal circuit after
cannulation of two central veins. In this circuit an artificial membrane
enables an extracorporeal gas exchange across the hollow fibres. vvECMO is
indicated in patients with severe ARDS within 7 days after onset and with
persistent life-threatening hypoxaemia despite optimised supportive therapy. Venovenous
extracorporeal CO2 removal (ECCO2R) is an ECMO technique that works at lower
extracorporeal blood and sweep gas flows than vv– and avECMO, which is mainly used
to avoid unacceptable hypercapnia or acidosis, as such preventing the need for injurious
ventilator settings (Morimont et al. 2014). All ECMO techniques implicate
certain haemodynamic effects and risks and their use requires expertise,
experience, routine and an interdisciplinary approach (Combes et al. 2014).
Possible complications include technical problems (clotting, air leakage,
haemolysis) as well as bleeding due to cannula insertion or systemic
anticoagulation. Despite the fact that technical advances have promoted safety and
simplicity of extracorporeal lung support systems during the past few years,
rigorous evidence of optimal indication, timing and management is still
lacking. Nevertheless ECMO is increasingly being used as a rescue therapy in
ARDS patients, and it might show a survival benefit in future randomised
studies.

Trauma
patients with critical hypoxaemia and/ or hypercapnic acidosis are at risk for
pulmonary and cardiocirculatory failure, especially with concomitant
haemorrhagic complications or anaemia. Furthermore, invasive mechanical ventilation
in ARDS may induce harmful effects of high inspiratory pressure and lung
overinflation to the right ventricle (Repesse et al 2015). Although there is a
rationale for the use of ECMO in these clinical situations, ECMO is seen as an
invasive measure with potentially severe complications, and in the early posttraumatic
period patients are in a fragile balance at risk of haemodynamic instability or
shock. In recent years, the feasibility and efficacy of ECMO in severe
posttraumatic ARDS was described by a few observational studies (a synopsis is
presented in Table 1). Cordell-Smith et al. published a retrospective analysis of
a cohort of 28 trauma patients with long bone fractures, blunt chest trauma or
combined injuries referred to a single tertiary centre for ECMO support (Cordell-Smith
et al. 2006). The survival rate in this group was 71.4%.

The experiences of the
Regensburg ECMO group were reported in 2013 (Ried et al. 2013). 52 trauma
patients with a mean age of 32 ± 14 years suffering from severe thoracic trauma
and ARDS were provided with pumpless arteriovenous extracorporeal lung support (PECLA
n=26) or with vvECMO (n=26). After applying ELS critical hypoxaemia and
hypercapnia were resolved immediately and the parameters of mechanical
ventilation were reduced in order to perform lung protective ventilation. The
mean duration of ELS support was 6.9 ± 3.6 days. During ECMO treatment numerous
thoracic and non-thoracic surgical procedures were necessary, but in this
series no relevant life-threatening bleeding complications were observed.
Similarly Guirand et al. reported data from two American College of
Surgeons-verified level 1 trauma centres (Guirand et al. 2014). Trauma patients
were divided retrospectively into a cohort of hypoxaemic patients, who received
vvECMO after failure of ‘conventional’ rescue (n=26), and into a patient group
managed with mechanical ventilation (n=76). In a matched-pair analysis the
adjusted survival rate was greater in the ECMO group (adjusted OR 0.193,
p=0.034), but ECMO patients received more transfusions and had more bleeding
complications. Finally the recent analysis of the Extracorporeal Life Support
Organization (ELSO) database on ECMO in 85 trauma patients (Jacobs et al. 2015)
demonstrated a survival to discharge of 74.1%. The general conclusion was that
the use of ELS might be advantageous in patients with post-traumatic ARDS. An
algorithm for the use of ECMO in trauma patients is given in Figure 1.

Practical Aspects and
Clinical Challenges

The use of ECMO in trauma patients is associated with
specific requirements and possible problems. It is a challenge for a high-level
trauma centre. Some practical aspects and specific clinical strategies must be
considered and should be reflected in an algorithm for the ICU team (Table 2).

Haemodynamic Monitoring and Therapy

Haemodynamic monitoring includes continuous monitoring of
arterial blood pressure, repeated echocardiography and continuous recording of
extracorporeal blood flow. Of note, pulse contour analysis-based or continuous thermodilution-based
cardiac output monitoring are not recommended in patients under ECMO, since the
first may underestimate cardiac output (Haller et al. 1995), and the second may
lead to erroneous results caused by indicator loss into the extracorporeal
circuit (Rauch et al. 2002). Accurate record of the cumulative fluid seems
important, since a positive cumulative fluid balance has been identified as one
independent predictor of worsened outcome of ECMO patients (Schmidt et al.
2014).

The demand for systemic anticoagulation to prevent circuit
clotting might favour bleeding complications. On the other hand continuous technical
advances (heparin-coated circuits, centrifugal pump) have reduced the required doses
for anticoagulation and allowed use even in severe trauma patients with
bleeding shock (Arlt et al. 2010). In the Regensburg ECMO Centre experience
(Ried et al. 2013) the continuous anticoagulation with heparin was balanced,
aimed at a target partial thromboplastin time (aPTT) ≈ 50 sec, and no severe bleeding
complications — even under thoracic and non-thoracic surgeries — were observed. The median demand of packed red blood cells was
3 (range 0-54) during the ECMO period. In patients with severe ARDS, who are
suffering from traumatic brain injury and intracranial bleeding, ECMO therapy
is considered to be contraindicated due to limited systemic heparinisation. On
the other hand these patients might benefit from ELS to avoid hypercapnia (increase
of intracranial pressure) and deleterious ventilation. The use of prolonged
heparin-free ECMO was reported in three multiple-injured ARDS patients with
traumatic brain injury (Muellenbach et al. 2012), and neither ECMO-associated
bleeding nor clotting of the extracorporeal circuit occurred. Such a
heparin-free ECMO strategy might be considered individually under specific
rescue conditions in an interdisciplinary round.

Intrahospital
Transportation and Damage Control Surgery

In the early post-traumatic period patients frequently need
transportation from the intensive care unit to diagnostic (e.g., CT scan,
interventional radiology, Figure 2) or therapeutic procedures (damage control
surgery, neurosurgery, laparotomy). In ECMO patients these transportations and
procedures are at special risk of ECMO-related or general complications and
they require special preparation and realisation. The following safety aspects
and recommendations are given (Day 2010):

For surgery procedures a careful balance between volume
replacement and avoidance of fluid overload must be ensured by experienced anaesthetists.
Systemic anticoagulation should be stopped for surgery. In the scenario of the
operating theatre, the ECMO cannulae are included in a sterile covering and
special attention is required to avoid accidental removal. The results from
recent observational studies (Cordell-Smith et al. 2006; Ried et al. 2013; Guirand
et al. 2014; Jacobs et al. 2015) show that diagnostic and therapeutic
procedures are associated with a low complication rate.

Conclusion

The technique of extracorporeal lung support is a promising
and life-saving treatment option in severe post-traumatic ARDS. ELS enables a rapid
and sustained improvement of critically impaired gas exchange and the
correction of severe acidosis, and additionally can provide lung protective
ventilation. Utilisation of ELS in multiple trauma patients is associated with
an acceptable complication profile, but a specific expertise, routine, and an
interdisciplinary approach are needed.

Conflict of Interest

Thomas Bein received honoraria for lectures and for the
membership of the Medical Advisory Board of Novalung Company, Heilbronn, Germany.

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